This invention relates to dead track recovery and improved strobe generation in recovering data from data processing equipment having parallel data channels.
Often the data bits of a particular data character are missing on a channel or track because of recording head failure or other causes. The data cannot be recovered satisfactorily when such data bits are missing. The present invention provides means for detecting such a dead track and for generating a simulated data bit that can be inserted when a data bit is missing from a data character. The most common technique of strobe generation is to generate a strobe delay signal that is fixed to approximately one-half cell time between input data bits. A disadvantage of utilizing such a fixed delay time is that there can never be more than a half-cycle (1/2 cell time) of skew between any two channels. The present invention provides improved strobe generation by generating a simulated clock track and deriving the strobe signals from the clock track. The clock track generates a group of periodic signals and strobe signals whose occurrence is functionally related to the period of the group of periodic signals. Means are provided for detecting the cell time between incoming data characters and changing the time period of the group of output signals generated, hence changing the delay of the generated strobe signals. The clock track generator averages the data bit scatter of the data characters over a predetermined number of characters and changes the clock frequency in order to change the period of the strobe signal delay. The clock track generator utilizes the average bit scatter and attempts to generate the strobe signal at one-half cell time of the average cell time of the data characters.
Accordingly, one primary feature of the present invention is to provide means for recovering a dead track in parallel data transmission.
Another feature of the present invention is to provide a dead track recovery means that can detect the absence of a necessary bit in one of said parallel data bit channels, generate a simulated data bit in response thereto, and selectively apply the simulated data bit to the parallel data bit channel missing the necessary data bit.
Yet another feature of the present invention is to provide means for simulating a clock track and generating strobe signals in combination with the dead track recovery circuit that provides means for controlling the periodic interval of the strobe signals.